Currently, there is known an audio device configured to: receive an audio signal from a reproduction device configured to reproduce an audio signal via a wireless network through use of a wireless network system; and amplify and output the received audio signal (see, for example, PTL 1). In recent years, there is also known an audio system including such an audio device as described above and a mobile terminal device, e.g., a cellular phone. In the above-mentioned audio system, the mobile terminal device and the audio device are connected to each other through a wireless network, and the audio device receives an audio signal transmitted from the mobile terminal device, amplifies the audio signal, and outputs the audio signal from a speaker. With such a related-art audio system, adjustment of volume or selection of a song of the audio signal output by the audio device can be arbitrarily changed remotely through operation of the mobile terminal device.
Such an audio system configured to transmit and receive the audio signal through the wireless network system does not require a reproduction device and a speaker device to be connected to each other through a signal cable unlike the related art. Therefore, there is no need to fix an installation place of the audio device, and a user is allowed to change the installation place of the audio device freely depending on an installation position and a listening position that are desired by the user, and to arbitrarily set the volume and the selection of the song of the audio signal output from the audio device by operating the mobile terminal device at a place distant from the audio device. Thus, the use can enjoy the audio signal output from the audio device.